This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A251780 #23 Feb 16 2025 08:33:24
%S A251780 1,6,3,7,6,6,4,6,9,1,6,3,7,6,6,4,6,9,1,6,3,7,6,6,4,6,9,1,6,3,7,6,6,4,
%T A251780 6,9,1,6,3,7,6,6,4,6,9,1,6,3,7,6,6,4,6,9,1,6,3,7,6,6,4,6,9,1,6,3,7,6,
%U A251780 6,4,6,9,1,6,3,7,6,6,4,6,9,1,6,3,7,6,6,4,6,9,1,6,3,7,6,6,4,6,9,1,6,3,7,6,6,4,6,9
%N A251780 Digital root of A069778(n-1) = n^3 - n^2 + 1, n >= 1. Repeat(1, 6, 3, 7, 6, 6, 4, 6, 9).
%C A251780 Periodic with cycle of 9: {1, 6, 3, 7, 6, 6, 4, 6, 9}.
%C A251780 The decimal expansion of 54588823/333333333 = 0.repeat(163766469).
%H A251780 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/DigitalRoot.html">Digital Root</a>.
%H A251780 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 1).
%F A251780 a(n) = digital root of n^3 - n^2 + n.
%e A251780 For a(3) = 3 because 3^3 - 3^2 + 3 = 27 - 9 + 3 = 21 with digit sum 3 which is also the digital root of 21.
%t A251780 LinearRecurrence[{0, 0, 0, 0, 0, 0, 0, 0, 1},{1, 6, 3, 7, 6, 6, 4, 6, 9},108] (* _Ray Chandler_, Jul 25 2016 *)
%o A251780 (PARI) DR(n)=s=sumdigits(n);while(s>9,s=sumdigits(s));s
%o A251780 for(n=1,100,print1(DR(abs(n^2-n-n^3)),", ")) \\ _Derek Orr_, Dec 30 2014
%Y A251780 Cf. A069778, A251754, A010888, A056992, A073636.
%K A251780 base,nonn,easy
%O A251780 1,2
%A A251780 _Peter M. Chema_, Dec 08 2014
%E A251780 More terms from _Derek Orr_, Dec 30 2014
%E A251780 Edited: name changed; formula, comment and example rewritten; digital root link added. - _Wolfdieter Lang_, Jan 05 2015